1. Technical Field
The present invention relates to metal interconnect in semiconductor devices, and more particularly, to metal seed layer deposition.
2. Related Art
Copper (Cu) is usually used as an interconnect material in semiconductor devices. Usually, if a copper region is to be electrically coupled to a target region (e.g., a drain/source region of a semiconductor transistor), a diffusion barrier layer (which is electrically conducting) is first applied to the target region, and then the copper region is applied to the diffusion barrier layer. In other words, the copper region and the target region are physically separated by the diffusion barrier layer. As a result, the diffusion barrier layer prevents copper atoms of the copper region from diffusing into the target region. Usually, the copper region is applied to the diffusion barrier layer in two steps. The first step comprises applying a thin layer (called seed layer) of copper to the surface of the diffusion barrier layer. The second step comprises applying a bulk layer of copper to the seed layer so that both the seed layer and bulk layer merge to form the copper region. The quality of the seed layer greatly affects the quality of the copper region. For instance, if the seed layer adheres well to the diffusion barrier layer, so does the resulting copper region.
Therefore, there is a need for a novel structure of a good seed layer. Also, there is a need for a method of forming the good seed layer.